Phase Selection Logic - ABB 615 series Technical Manual

1MAC059074-MB A
5.7.4.1
615 series ANSI
Technical Manual
The operation of 21FL can be described with a module diagram. All the modules in the
diagram are explained in the next sections.
I_A
I_B
Phase
I_C
selection
logic
V_A_AB
V_B_BC
V_C_CA
I
Trigger
0
I detection
1
I
2
V
0
V
1
V
2
TRIGG
TRIGG_XC0F
BLOCK
GUID-5DEC6352-438F-4B66-88F1-F72C0138AECF V1 EN
Figure 410: Functional module diagram

Phase selection logic

Identification of the faulty phases is provided by the built-in Phase Selection Logic based
on combined impedance and current criterion. Phase selection logic is virtually setting-
free and has only one parameter, Z Max phase load, for discriminating a large symmetrical
load from a three-phase fault. The setting Z Max phase load can be calculated using the
equation.
Z Max phase load = 0 8 .
GUID-BDFF7D0D-9323-4610-84C6-A9B4234136B3 V1 EN
V Nominal phase-to-phase voltage
xy
S Maximum three-phase load
max
For example, if V = 20 kV and S
xy
The identification of the faulty phases is compulsory for the correct operation of 21FL.
This is because only one of the impedance-measuring elements (fault loops) provides the
correct result for a specific fault type. A three-phase fault is an exception and theoretically
ALARM
Fault
impedance
and
Recorded
distance
calculation
Alarm
indication
2
V
xy
⋅
S
max
= 1 MVA, then Z Max phase load = 320.0 Ω.
max
Protection related functions
data
Section 5
(Equation 137)
805